1. Field of the Invention
The present invention relates to a polishing apparatus for polishing workpieces by means of a polishing tool.
2. Description of the Related Art
A variety of components having spherical surfaces and complex curved surfaces are used in various industrial fields. Some of them, such as optical lenses and X-ray reflectors, have high-precision curved mirror surfaces.
One method of forming such mirror surfaces is the high-precision polishing method, in which a soft polishing tool made of plastic or rubber is used to polish workpieces with high precision. The polishing tool can have either a concave or a convex surface. A workpiece is placed in contact with the polishing surface of the polishing tool, and is polished thereby.
Recently, an automatic high-precision polishing apparatus has been developed. This apparatus comprises an NC controller, a tool for polishing a workpiece, an electric motor for driving the tool under the control of the NC controller, and a mechanism for supporting the tool and applying a load from the work point of the tool to the surface of the workpiece, under the control of the NC controller. The NC controller controls the motor in accordance with coordinates data representing the positions which the tool must take with respect to the workpiece, thereby moving the tool to a desired position.
In order to polish the workpiece uniformly over its entire surface, it is necessary for the tool to apply a constant load from its work point to the surface of the workpiece, at all times during the polishing. The tool, however, cannot be moved so minutely as to move its work point along the peaks and depressions formed in the surface of the workpiece, which have heights and depths in the order of nanometers, and inevitably fails to apply the same load to every part of the workpiece surface. The parts of the workpiece are polished with different loads, and come to have different surface roughnesses.